A brief description will be given of a Third Generation Partnership Project Long Term Evolution (3GPP LTE) (hereinafter, referred to as “LTE”) communication system, which is an example of a wireless communication system to which the present invention is applicable.
FIG. 1 is a view schematically showing a network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as an example of a wireless communication system. The E-UMTS system has evolved from the conventional UMTS system and basic standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, refer to Release 7 and Release 8 of “Third Generation Partnership Project; Technical Specification Group Radio Access Network,” respectively.
Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG), which is located at an end of a network (E-UTRAN) and is connected to an external network. eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One or more cells may exist per eNB. A cell is configured to use one selected from among bandwidths of 1.25, 2.5, 5, 10, 15, and 20 Mhz to provide a downlink or uplink transport service to several UEs. Different cells may be configured to provide different bandwidths. The eNB controls data transmission to and data reception from a plurality of UEs. The eNB transmits downlink scheduling information with respect to downlink (DL) data to notify a corresponding UE of a time/frequency domain in which data is to be transmitted, coding, data size, and Hybrid Automatic Repeat and reQuest (HARQ)-related information. In addition, the eNB transmits uplink scheduling information with respect to uplink (UL) data to a corresponding UE to inform the UE of an available time/frequency domain, coding, data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A Core Network (CN) may include the AG and a network node for user registration of the UE. The AG manages mobility of a UE on a Tracking Area (TA) basis, wherein one TA includes a plurality of cells.
Although wireless communication technology has been developed up to LTE based on Wideband Code Division Multiple Access (WCDMA), demands and expectations of users and providers continue to increase. In addition, since other radio access technologies continue to be developed, new technology is required to secure competitiveness in the future. For example, decrease of cost per bit, increase of service availability, flexible use of a frequency band, simple structure, open interface, and suitable power consumption by a UE are required.